Normally, applications are installed from our App Store as described here. However, if you have downloaded an .apk file to your computer, you can install it via a USB connection. There are two mechanisms for this.
Without Additional Software
For the M300XL: Disconnect the battery from the M300XL to expose the USB Micro-B port.
For the M300: Attach either a USB Micro-B adapter or the a battery to the custom connector to expose the USB Micro-B port.
Insert a USB-A to USB Micro-B cable between the device and a USB-3.1 high-power port on the computer. Standard USB ports on the computer do not supply sufficient power and cannot be used.
On the M-Series device, open Settings > Storage & USB.
Long-press the front button to show the menu.
Select USB Mode.
Change the mode to File transfers. The M300 should appear as a device on your computer.
Use your Windows File Explorer or macOS Finder to copy the .apk file to the virtual SD Card of the device.
On the M-Series device, open Settings > Storage & USB > explore.
Locate the file you copied.
Highlight the .apk file and click it to install.
Using Android Debug Bridge Software
If not already installed, obtain ADB software from developer.android.com. Follow the setup procedure so that adb is in your path. Simply issue the command ‘adb install <path to file>.apk’ in a command window.